Currently, many cameras (i.e., imaging apparatuses) can capture both a moving image and a still image. There are many products in which a moving image capturing mode and a still image capturing mode are switched via a mechanical switch or the like. More specifically, when a user intends to capture the moving image, the user switches the mechanical switch to the moving image capturing mode, and then presses a moving image capturing start trigger button. When the user intends to capture the still image, the user switches the mechanical switch to the still image capturing mode, and then presses a still image capturing trigger button. However, as a stress free imaging apparatus, it is desirable to allow the moving image or the still image to be captured without switching the mechanical switch or the like.
Accordingly, a currently adopted switching method is as follows. The imaging apparatus is normally operated with the moving image capturing mode and when the still image capturing trigger button is pressed, the still image is captured by switching the mode to the still image capturing mode. After the still image is captured, when any operation is not performed for a predetermined time, the mode returns to the moving image capturing mode again. In such a case, conventionally, when the still image is captured, an autofocus operation is performed after exposure control is determined. This is a reasonable order because, in the exposure control, when a diaphragm is operated, depth of field is changed due to a change in the aperture diameter of the diaphragm. This is a technique that allows the exposure control and the autofocus control to be accurately performed. This technique is discussed in Japanese Patent Application Laid-Open No. 2001-281530.
However, since the autofocus control is executed after the exposure control, a release time lag Tlg is determined by the following equation:Tlg=Tex+Tfo+Tcl  (1)
where exposure control time is Tex, autofocusing time is Tfo, and mechanical shutter close time is Tcl.
If the exposure control and the focus control are executed based on an image signal output from an image sensor, the control is performed with feedback control. Thus, the exposure control time Tex of approximately 0.5 sec. and the autofocusing time Tfo of approximately 0.5 sec are required.
Further, the mechanical shutter close time is 0.005 sec. Thus, the exposure control time Tex and the autofocus time Tfo are dominant in the release time lag Tlg. The release time lag may cause a shutter opportunity miss.